HSCI 3013 Exercise 7

Peter Barker

Tycho's problems with orbs

In 1588, Tycho Brahe published a new system of the world. Keeping the earth as the center of the cosmos, the moon and the sun both revolve around the earth, as in Ptolemy's system. But all the other planets have motions centered on the sun, and are carried around with it, in the same way that the moon is carried around with the earth in Copernicus's system.

Question 1: Ignoring the moon, use the distances provided for Copernicus in the previous exercise to draw the inner part of Tycho's system, with the earth in the center, the sun going around the earth, and Mercury and Venus going around the sun. If the physical orb of the sun must be thick enough to accommodate the orbs you have drawn for Mercury and Venus, what must its inner and outer radii be?

Question 2: On the same diagram draw in the maximum and minimum distances for Mars. Be sure your diagram shows what happens on the opposite side of the earth from the sun. If the orbs we have drawn so far are treated as solid objects, is there anything wrong with this picture? If the orbs are treated as no more than geometrical boundaries in a continuous fluid medium, can Mars and the Sun ever collide?